Constraining Dark Energy with the Supernova Legacy Survey
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Constraining Dark Energy with the Supernova Legacy SurveyMark Sullivan University of Toronto
http://legacy.astro.utoronto.ca/http://cfht.hawaii.edu/SNLS/
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Paris GroupReynald Pain, Pierre Astier, Julien Guy, Nicolas Regnault, Christophe Balland, Delphine Hardin, Jim Rich, + UKGemini PI: Isobel Hook, Richard McMahon, + USALBL: Saul Perlmutter, + CIT: Don NeillFull list of collaborators at: http://cfht.hawaii.edu/SNLS/ Victoria GroupChris Pritchet, Dave Balam, + Toronto GroupRay Carlberg, Alex Conley, Andy Howell, Kathy Perrett, Mark Sullivan The SNLS collaborationMarseille GroupStephane Basa, Dominique Fouchez, +
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White DwarfSNe Ia are thermonuclear explosions of C-O white dwarf starsStandard nuclear physicsBright: 10 billion sunsStandardizable: 7% calibrationBrightness and homogeneity make them the best measure of distance, and hence dark energy, in the Universe
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Supernova Legacy Survey (2003-2008)Megaprime5 year survey, goal: 500 distant SNe Ia to measure wUses CFHT/Megacam36 CCDs, good blue response4 filters for good k-corrections and color measurement
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CFHT-LS OrganisationSNLS collaborationData-processing
Major Spectroscopic ProgramGemini (Canada/UK/USA)120 hrs/yr (60:40:20)VLT (France/Other Euros)120 hrs/yrKeck (through LBL)40 hrs/yrCosmological analysesMagellan near-IR study (Freedman et al.)Rest-frame I-band Hubble diagramKeck SN Ia UV study (Ellis/Sullivan et al.)LRIS high-S/N - metallicity through UV linesTesting accuracy of k-corrections in the UVSN IIP study (Nugent/Sullivan/Ellis et al.)Using SNe IIP as standard candlesIndependent Hubble diagram to z=0.5
CFHT-LS (imaging) 2003-2008DEEPWIDEGalaxy studiesTime sequenced dataset (202n over 5 years)Cosmic shearClusters
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Supernova Legacy SurveyKeck (8 nights/yr)Gemini N & S (120 hr/yr)VLT (120 hr/yr)Magellan (15 nights/yr)Imaging
Distances fromlight-curvesSpectroscopy
Redshifts Distances from cosmological modelDiscoveriesLightcurvesgriz every 4 days during dark time
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k-corrections in SNLS
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k-corrections in SNLS
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Making a standard candle1. Phillips relation: A correction to SN Ia light-curves based on light-curve shape drastically improves the quality of the standard candle.Time Brightness Brightness Time 56Ni 56Co 56Fe powers the SN Ia light-curveConventional Wisdom:SNe are a one-parameter family defined by amount of 56Ni synthesized in the explosion. More 56Ni greater luminosity higher Temperatures higher opacity broader LC
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Colour at peakMaking a standard candle1. Phillips relation: A correction to SN Ia light-curves based on light-curve shape drastically improves the quality of the standard candle.2. SN colour: A correction to the SN luminosity based on the SN colourBlueRedFainter
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Making a standard candle1. Phillips relation: A correction to SN Ia light-curves based on light-curve shape drastically improves the quality of the standard candle.Brightness Brightness Time 20%7%!Many methods:Stretch Perlmutter 97, 99(M)LCS(2k2) Riess, 95,96, Jha 07SALT(2) Guy 05, 07SiFTO Sullivan 07CMAGIC Wang et al.; Conley 06m15 Phillips 93; Hamuy 95; Prieto 062. SN colour: A correction to the SN luminosity based on the SN colour
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Local SN Ia Hubble DiagramsJha et al. 2007Prieto et al. 2006Most light-curve fitting techniques fare equally well
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Light-curve fit parameters from different fitters are tightly correlated
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A Typical SN
What we need to measurePeak brightnessLightcurve width (stretch)Colour (c)
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SNLS: Current statusSurvey running for 3.5 years~310 confirmed distant SNe Ia (+ 40-50 not yet processed)~ Largest single telescope sample of SNeOn track for 500 spectroscopically confirmed SNe Ia by survey end (>1000/>2000 total SNIa/All SN light-curves)
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Rolling light-curves
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SNLS 1st yearM = 0.263 0.042 (stat) 0.032 (sys)=-1.02 0.09 (stat) 0.054 (sys)Astier et al. 2006349 citations(187 in refereed journals)
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Third year SNLS Hubble Diagram (preliminary)Preliminary3/5 years of SNLS~240 distant SNe IaIndependent analysis to 1st year:Different calibration routeDifferent photometric methodsDifferent SN light-curve analysis toolsSullivan et al. 2007
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Third year SNLS Hubble Diagram (preliminary)M=0.3, =0M=1.0, =0Best-fit for SNLS+flatnessPreliminary(error was 0.042 in A06)Sullivan et al. 2007
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Cosmological Constraints (Preliminary)SNLS+BAO (No flatness)SNLS + BAO + simple WMAP + FlatBAOBAOSNeSNeWMAP-36-7% measure of Sullivan et al. 2007
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Future Prospects with SNLSCurrent constraints on : =-1 to ~6-7% (stat)
>-0.8 excluded at 3-sigma level
At survey end a 4-5% statistical measure will be achieved:500 SNLS + 200(?) SDSS + new local samplesImproved external constraints (BAO, WMAP, WL)
Systematic errors becoming ever more important
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Potential SN Systematics in measuring w(a)Experimental SystematicsCalibration, photometry, Malmquist-type effects
Contamination by non-SNe IaMinimized by spectroscopic confirmation
K-correctionsUV uncertain; golden redshifts; spectral evolution?
Non-SNe systematicsPeculiar velocities; Hubble Bubble; Weak lensingExtinctionEffective RB; Dust evolution
Redshift evolution in the mix of SNePopulation drift environment?
Evolution in SN propertiesLight-curves/Colors/LuminositiesMore mundaneMore scientifically interesting
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Hubble BubbleLatest MLCS2k2 paper (Jha 2007)MLCS2k2 attempts to separate intrinsic colour-luminosity and reddening
3 decrease in Hubble constant at 7400 km/sec local value of H0 high; distant SNe too faint
Local void in mass density?
Could have significant effects on w measurementMLCS2k2SALTNo Bubble with other light-curve fitters!Conley et al. (2007)
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Light-curve fit parameters from different fitters are tightly correlated
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Handling colour in SN IaColour is the most important correction to SN Ia luminositiesUnderlying physics: Redder SNe Ia are fainter due toExtinction along the line of sightIntrinsic luminosity/colour relationship of the SN population
Two basic approaches:Attempt to identify intrinsic relationship and assume standard dust dominates the rest (Jha et al.)
Fit a luminosity/colour relationship empirically on the SN data=4.1
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Bubble significance versus Conley et al. (2007)
- All fitters agree:
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What does =2 (RV=1) mean?Very strange dust? But RV=1 is not seen anywhere in the Milky WayDust around SNe is changed by the explosion?
Most likely: SNe have an (as yet) uncorrected-for intrinsic colour-luminosity relationship
While fitting empirically for may be empirical, currently its the best way
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Potential SN Systematics in measuring w(a)Experimental SystematicsCalibration, photometry, Malmquist-type effects
Contamination by non-SNe IaMinimized by spectroscopic confirmation
K-correctionsUV uncertain; golden redshifts; spectral evolution?
Non-SNe systematicsPeculiar velocities; Hubble Bubble; Weak lensingExtinctionEffective RB; Dust evolution
Redshift evolution in the mix of SNePopulation drift environment?
Evolution in SN propertiesLight-curves/Colors/LuminositiesMore mundaneMore scientifically interesting
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Potential SN Systematics in measuring w(a)Experimental SystematicsCalibration, photometry, Malmquist-type effects
Contamination by non-SNe IaMinimized by spectroscopic confirmation
K-correctionsUV uncertain; golden redshifts; spectral evolution?
Non-SNe systematicsPeculiar velocities; Hubble Bubble; Weak lensingExtinctionEffective RB; Dust evolution
Redshift evolution in the mix of SNePopulation drift environment?
Evolution in SN propertiesLight-curves/Colors/LuminositiesPopulation Evolution
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?White DwarfMany uncertainties: Nature of progenitor system the second star Single versus double degenerate? Young versus old progenitor? Explosion mechanism? Effect of progenitor metallicity on luminosity?
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Host galaxies impact SN propertiesSome evidence that SNe Ia in ellipticals show smaller scatterSullivan et al. (2003)e.g. Hamuy et al. (2000)SN Ia Light-curve shape depends on morphologyLow stretchHigh stretch
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PassiveStar-formingStarbursting Little morphological information available
CFHT u*griz imaging via the Legacy program.
PEGASE2 is used to fit SED templates to the optical data.
Recent star-formation rate, total stellar mass, mean age are estimated.
Hosts classified according to physical parameters instead of what they look like.Typing of SNLS SN Ia hostsSullivan et al. (2006)
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SNLS: SN rate as a function of sSFRSN Ia hosts classified by star-formation activity
Per unit stellar mass, SNe are at least an order of magnitude more common in more vigorously star-forming galaxiesSNLS passive galaxies
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SNLS selection of hostsD2 ACS imaging
Plenty of irregular/late-type systems
Few genuine ellipiticals
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SN Ia Stretch dependencies170 SNe Ia(Update from Sullivan et al. 2006; better zeropoints, host photometry, more SNe)PassiveStar-formingStretch versus mean ageStretch by galaxy star-formation activityThe majority of SN Ia come from young stellar populations
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Recent SNLS evidence for two components for SNe IaOlder progenitor SNe
Empirically, SN Rate is proportional to galaxy mass
Preferentially found in old stellar environmentsTypically fainter with faster light-curves (low stretch)Younger progenitor SNe
Empirically, SN rate is proportional to galaxy star formation rate
Exclusively found in later type star-forming galaxiesTypically brighter with slower light-curves (high stretch)(Extreme example: SNLS-03D3bb?)
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Recent SNLS evidence for two components for SNe IaOlder progenitor SNe
Empirically, SN Rate is proportional to galaxy mass
Preferentially found in old stellar environmentsTypically fainter with faster light-curves (low stretch)Younger progenitor SNe
Empirically, SN rate is proportional to galaxy star formation rate
Exclusively found in later type star-forming galaxiesTypically brighter with slower light-curves (high stretch)(Extreme example: SNLS-03D3bb?)Could evolution between the two components with redshift distort the dark energy signal?
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SN population drift?Relative mix of evolves with redshift
A+B predictions, but similar for any two component model
Sullivan et al. 2006
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Stretch versus redshift (3rd year)?
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Evolution in Stretch?
Gaussians predicted evolution from A+B model
Average stretch, and thus average intrinsic brightness of SNe Ia evolves with redshift
but
if stretch correction works perfectly, this should not affect cosmologyHowell et al. 2007Nearbyz1
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Effect on cosmologyExtreme case using SNLS 1st year
Use only s0.4
Effects of evolution smaller than error budget for determination of , must be studied closely to determine the effect on measuring w(a)SNLS yr 1 N: 115 = 1.6 = 1.8w = -1.05 0.09M = 0.27 0.02Yr 1 s split N: 56 = 1.4 = 1.8w = -0.92 0.15M = 0.28 0.03
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Split by s (preliminary)
SM0.95
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Stretch correction across environmentsConley et al. 2006No evidence for gross differences between light-curves in passive and active galaxiesRest-frame B composite light-curve
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Morphological Hubble diagram
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Split by host galaxySN SubsetsProblems: Low-redshift sample very small, Malmquist correction likely to be differentPassiveStar-forming=1.34 0.25=2.52 0.2~0.10 mag=-0.880.11=1.19 0.15=2.71 0.2~0.140 mag =-1.040.08Preliminary
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Do SNe Ia Evolve? UV Spectrum Probes MetallicityLentz et al. (2000)
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High S/N spectra of SNLS SNeEllis, Sullivan et al. 2007
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Light-curve width dependenceImplications for JDEM: k-corrections must improve in accuracy
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SummarySNLS is a well-controlled, calibrated and understood experiment
Current SN Ia measurement determine to ~ 6-7%SNLS is the best cosmological SN Ia dataset available
In 2-3 years, 4-5% will be achieved
Colour is the critical correction to SN Ia distances; currently can only be handled empirically
SNe Ia have a range of progenitor agesImpacts on light-curve shape: faster/older & slower/younger
SNe in passive galaxies are better standard candles?More homogeneous stellar population? Less dust?
Point is: look at diversity of host types!